1. Field
Embodiments of the present disclosure relate to an infrared sensor module capable of measuring a distance to an obstacle (object) using an infrared sensor.
2. Description of the Related Art
Generally, a robot cleaner moves about a target area to be cleaned without receiving a control signal from a user and collects foreign matter, such that it can automatically clean the target area. The robot cleaner measures the distance from the robot cleaner to an obstacle (object) (for example, furniture, office equipment, and walls) installed in the target area through an obstacle sensor, and moves about the target area without colliding with the obstacle using the measured distance information, thereby cleaning the target area.
A variety of sensors may be used as the obstacle sensor, for example, an ultrasonic sensor, a Position Sensitive Detector (PSD) sensor, an infrared sensor, etc. The most popular obstacle sensor from among the above-mentioned sensors is the infrared sensor because the infrared sensor is cheapest.
FIG. 1 is a schematic diagram illustrating an arrangement of a light emitting unit and a light receiving unit contained in a conventional infrared sensor. Referring to FIG. 1, the infrared sensor 10 generally includes a light emitting unit 11 having an infrared light emitting diode (IRED) for emitting infrared light, and a light receiving unit 12 including a photo resistor (PTR) or photo diode (PD) to detect the amount of reflected light. The infrared sensor 10 detects the light amount generated when the light emitted from the light emitting unit 11 is reflected from the surface of the object and is then incident upon the light receiving unit 12, and measures the distance from the infrared sensor 10 to the object using the detected light amount. In this case, the light emitting unit 11 and the light receiving unit 12 of the infrared sensor 10 are arranged in such a manner that, when the infrared sensor 10 gradually approaches the object or the object approaches the infrared sensor 10, the distance from the infrared sensor 10 to the object is decided such that a characteristic curve of the reflected light obtained at the center point (i.e., a horizontal diagonal point of a diamond shape shown in FIG. 1) of the reflected-light-amount measurement section M reaches a peak point. Herein, the reflected-light-amount measurement section M is established in such a manner that the robot cleaner, which desires to detect the object (obstacle) or to move slowly, includes a specific distance (e.g., 20 mm) from the infrared sensor 10 to the object. Specifically, the specific distance is located in the vicinity of the maximum of the characteristic curve of the amount of reflected light in the reflected-light-amount measurement section M.
FIG. 2, parts (a) and (b), shows a circuit diagram illustrating a light emitting unit and a light receiving unit in the conventional infrared sensor. Referring to FIG. 2, part (a), the light emitting unit 11 includes a light emitting diode (IN_IRED), a current limiting resistor R1, and a light emitting control switching element (IN_CTRL_ON_OFF) for receiving on/off control signals of the light emitting diode (IN_IRED). Meanwhile, as shown in FIG. 2 part (b), the light receiving unit 12 includes a light receiving element (IN_PTR(NPN)), an output resistor (R2), and an output voltage terminal (V_OUT).
Ideally, although it is necessary for the light receiving unit 12 to detect the amount of light corresponding to the distance from the infrared sensor 10 to the object, the important matter in measuring the distance from the infrared sensor 10 to the object using the infrared sensor 10 is surface reflectivity (hereinafter referred to simply as ‘reflectivity’) depending on the object color. FIG. 3 is a graph illustrating the characteristic curve of the output voltage (the amount of reflected light) of the light receiving unit in response to both the distance from the infrared sensor to the object and reflectivity of each object. As can be seen from FIG. 3, the object (e.g., a white object) having reflectivity of 90% has a higher output voltage (greater reflected light amount or greater received light amount) as compared to another object having relatively low reflectivity (object having reflectivity of 18% or 3%). That is, the output voltage of the light receiving unit 12 changes depending upon the reflectivity of the object being sensed.
Assuming that the infrared sensor 10 is used as an obstacle sensor of the robot cleaner in such a manner that the robot cleaner stops motion and slowly moves at a position spaced apart from the object located ahead by a predetermined distance, the robot cleaner is implemented to stop motion or to slowly move upon receiving infrared light of more than a predetermined light amount. For example, if a comparison voltage (voltage corresponding to specific light amount) of FIG. 3 is set to 0.5V, it is determined that the object (white object) having a reflectivity of 90% has been detected at a specific position spaced apart from the infrared sensor 10 by 90 mm, and it is also determined that another object (gray object) having reflectivity of 18% has been detected at a specific position spaced apart from the infrared sensor 10 by 27 mm. In contrast, the robot cleaner never detects the object (black object) having reflectivity of 3%. That is, in order to detect a high-reflectivity object (e.g., a white object), the robot cleaner stops or slowly moves at a distance from the object. In order to detect a low-reflectivity object (e.g., a gray- or black-object), the robot cleaner may stop or slowly move at a position very close to the object, or the robot cleaner may sometimes collide with the object if no signal is received from the object.
As described above, the output voltage (the amount of reflected or received light) of the light receiving unit 12 is affected not only by the distance from the infrared sensor 10 to the object, but also by reflectivity of the object. Therefore, it is difficult for the conventional infrared sensor 10 to correctly recognize the distance from the infrared sensor 10 to the object only using the amount of light applied to the light receiving unit without considering reflectivity of the approaching object.